From U.S. Pat. No. 6,027,422 there is known a switchable synchronising device for a four-wheel drive vehicle. The synchronising device can be switched in such a way that it is suitable for a two-wheel drive and a four-wheel drive. For this purpose, there is provided a differential assembly with a switchable claw coupling which, in a closed condition, transmits torque to the differential and, in an open condition, interrupts a torque flow.
From DE 102 16 290 A1 there is known a similar differential mechanism which is suitable for changing from two-wheel drive to four-wheel drive. The differential mechanism comprises a differential drive, a coupling and an electromagnetic actuator for actuating the coupling.
Document DE 101 51 713 A1 proposes a differential system for a hybrid vehicle. The hybrid vehicle comprises a front wheel drive system with an internal combustion engine and a rear wheel drive system with an electric motor. Via a reduction gear, the electric motor drives an axle differential which transmits the torque to the lefthand and righthand sideshafts. There is provided a control system with a sensor for recording the driving condition and for generating a motor signal for the electric motor. Under normal driving conditions, the internal combustion engine drives the front wheels. If necessary, for example when starting or accelerating the vehicle or when the front wheels slip, the rear wheels are additionally driven by the electric motor.
From DE 10 2004 039 826 B4 there is known a clutch unit, wherein an engagement of a dog clutch can be restricted until a revolution of an input shaft and the revolution of an output shaft correspond to each other so as to be suitable for the engagement. Thus, torque can be reliably transmitted from the driving source to the wheels through a reduction mechanism.
From US 2008/0122436 A1 there is known an electromagnetic actuator assembly and a differential assembly that incorporates same. The electromagnetic actuator assembly comprises a frame, a movable plunger, first and second sensor targets that are coupled to a plunger for movements therewith, first and second sensors that are coupled to the frame and controller. The first and second sensors are configured to sense a position of the first, respectively the second sensor target and to produce a first and second sensor signal in response thereto.
Electric motors have a limited speed range and are therefore usually used as supplementary drives in a motor vehicle which, in addition to the electric motor, comprises an internal combustion engine as the main drive. Therefore, the electric motor is primarily used for low vehicle speeds for driving the vehicle, for instance in urban traffic where frequent starting and braking operations are required. Because of the relatively high torque values provided by the electric motor, there exist good traction conditions and a good starting behaviour. At higher vehicle speeds, for example during long distance driving, the electric motor is switched off, so that the drag moment of the electric motor does not adversely affect the efficiency of the motor vehicle and fuel consumption. For switching off the electric motor, use is made of a controllable coupling which is arranged in the driveline between the electric motor and the differential drive.
There is a need for a differential assembly, more particularly for a driving axle driven by an electric motor in the driveline of a motor vehicle, which differential assembly reliably identifies the switching condition of the coupling and which comprises a simple and space-saving design.